Implantable medical device having a sense channel with performance adjustment

ABSTRACT

An implantable medical device (IMD) may include a sensor for providing a sensor output signal and a sense channel configured to receive the sensor output signal from the sensor. The sense channel may be configured to process the sensor output signal and output a sense channel output signal. The sense channel may have an adjustable performance level, wherein for a higher performance level the sense channel consumes more power than for a lower performance level. A controller may be configured to adjust the performance level of the sense channel to achieve more performance and more power consumption when a higher degree of sense channel performance is desired and to achieve less performance and less power consumption when a higher degree of performance is not desired.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/413,726 filed on Oct. 27, 2016, the disclosureof which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure pertains to medical devices, and moreparticularly to implantable medical devices in which performance may beadjusted

BACKGROUND

Implantable medical devices are commonly used today to monitor and/ordelivery therapy to a patient. In one example, many patients suffer fromheart conditions that can result in a reduced ability of the heart todeliver sufficient amounts of blood to the patient's body. Such heartconditions may lead to slow, rapid, irregular, and/or inefficient heartcontractions. To help alleviate some of these conditions, variousmedical devices (e.g., pacemakers, defibrillators, etc.) can beimplanted in a patient's body. Such devices may monitor and in somecases provide electrical stimulation (e.g. pacing, defibrillation, etc.)to the heart to help the heart operate in a more normal, efficientand/or safe manner. In another example, neuro stimulators are often usedto stimulate tissue of a patient to help alleviate pain and/or someother condition. In yet another example, an implantable medical devicemay simply be a monitor that monitors one or more physiological or otherparameters of the patient, and to communicate the sensed parameters toanother device such as another implanted medical device or an externalprogrammer. To extend the effective lifetime of such implanted medicaldevices, there is a desire to conserve energy while still providingeffective monitoring and/or delivery of therapy to the patient.

SUMMARY

This disclosure describes implantable medical devices that include asense channel that can be dynamically adjusted to achieve a desiredperformance level based on the current conditions and/or current needs.A higher performance level will typically increase the power consumptionof the sense channel relative to a lower performance level. By settingthe performance level of the sense channel to an appropriate level, theeffective lifetime of the power supply of the implantable medical devicemay be extended.

In one example, an implantable medical device (IMD) may include ahousing, a sensor for providing a sensor output signal and a sensechannel that is configured to receive the sensor output signal from thesensor, process the sensor output signal, and output a sense channeloutput signal. The sense channel may have an adjustable performancelevel, wherein for a higher performance level the sense channel consumesmore power and for a lower performance level the sense channel consumesless power. The IMD may include a controller that is configured toreceive the sense channel output signal. In some cases, the controllermay be configured to adjust the performance level of the sense channelto achieve more performance and more power consumption when a higherdegree of performance is desired and to achieve less performance andless power consumption when a high degree of performance is not desired.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to determine a measure of a signal-to-noiseratio (SNR) of the sense channel output signal, and to adjust theperformance level of the sense channel based at least in part on themeasure of the signal-to-noise ratio (SNR) of the sense channel outputsignal.

Alternatively or additionally to any of the embodiments above, theperformance level of the sense channel may be adjusted by adjusting anoise floor of a sense amplifier of the sense channel.

Alternatively or additionally to any of the embodiments above, theperformance level of the sense channel may be adjusted by adjusting aresolution of the sense channel and/or a supply voltage of a senseamplifier of the sense channel.

Alternatively or additionally to any of the embodiments above, theperformance level of the sense channel may be adjusted by adjusting asample rate of the sense channel.

Alternatively or additionally to any of the embodiments above, the sensechannel may include a sense amplifier, and the performance level of thesense channel may be adjusted by adjusting a bias of the senseamplifier.

Alternatively or additionally to any of the embodiments above, the sensechannel is activated and deactivated at a duty cycle, and theperformance level of the sense channel may be adjusted by adjusting theduty cycle of the sense channel.

Alternatively or additionally to any of the embodiments above, the sensechannel samples the sensor output signal at a sample rate, and theperformance level of the sense channel may be adjusted by adjusting thesample rate of the sense channel.

Alternatively or additionally to any of the embodiments above, the sensechannel includes an analog-to-digital (A/D) converter with an adjustableresolution, and the performance level of the sense channel may beadjusted by adjusting the resolution of the A/D converter.

Alternatively or additionally to any of the embodiments above, the IMDis configured to sense and process two or more different cardiacsignals, and the controller may be configured to adjust the performancelevel of the sense channel based at least in part on which of the two ormore different cardiac signals is to be sensed and processed. In somecases, the two or more different cardiac signals include an R-wave and aP-Wave, and the controller may be configured to adjust the performancelevel of the sense channel to achieve more performance and more powerconsumption when the P-Wave is to be sensed and processed, and to adjustthe performance level of the sense channel to achieve less performanceand less power consumption when the R-Wave is to be sensed andprocessed.

Alternatively or additionally to any of the embodiments above, thecontroller may be configured to automatically and dynamically adjust theperformance level of the sense channel.

Alternatively or additionally to any of the embodiments above, the IMDmay be a leadless cardiac pacemaker (LCP).

Alternatively or additionally to any of the embodiments above, the IMDmay be an insertable cardiac monitor (ICM).

In another example, a leadless cardiac pacemaker (LCP) configured forimplantation into a patient's heart may be configured to senseelectrical cardiac activity and to deliver pacing pulses to thepatient's heart. The LCP may include a housing, a first electrode thatis secured relative to the housing and a second electrode that issecured relative to the housing and is spaced from the first electrode.A controller may be disposed within the housing and may be operablycoupled to the first electrode and the second electrode such that thecontroller is capable of receiving, via the first electrode and thesecond electrode, electrical cardiac signals of the heart. A sensor maybe disposed within the housing and may be configured to sense anindication of cardiac activity and provide a sensor output signal. Asense channel may be configured to receive the sensor output signal fromthe sensor, process the sensor output signal and to output a sensechannel output signal. In some cases, the sense channel may have anadjustable performance level, wherein for a higher performance level thesense channel consumes more power and for a lower performance level thesense channel consumes less power. The controller may be configured toreceive the sense channel output signal and to adjust the performancelevel of the sense channel to achieve more performance and more powerconsumption when a higher degree of performance is desired and toachieve less performance and less power consumption when a high degreeof performance is not desired.

Alternatively or additionally to any of the embodiments above, the LCPmay be configured to sense and process two or more different cardiacsignals, and the controller may be configured to adjust the performancelevel of the sense channel based at least in part on which of the two ormore different cardiac signals is to be sensed and processed.

Alternatively or additionally to any of the embodiments above, thesensor may include an electrical signal sensor that senses an electricsignal between the first electrode and the second electrode.

Alternatively or additionally to any of the embodiments above, thesensor may include one or more of an accelerometer, a pressure sensor, agyroscope, and a magnetic sensor.

In another example, a method of monitoring a patient's heart using animplantable medical device that is configured for implantation proximatethe patient's heart and that includes a sensor configured to sense anindication of cardiac activity, a dynamically adjustable sense channelconfigured to process a signal from the sensor, and a controlleroperably coupled to the dynamically adjustable sense channel. Theillustrative method includes sensing an indication of cardiac activityusing the sensor, the sensor outputting a signal to the dynamicallyadjustable sense channel. The dynamically adjustable sense channel isoperated at a performance level to process the signal from the sensorand output the processed signal to the controller. The processed signalmay then be analyzed for an indication of signal quality and adetermination may be made as to whether the indication of signal qualityis acceptable. The performance level of the dynamically adjustable sensechannel may be adjusted upward if the indication of signal quality isnot acceptable. In some cases, the performance level of the dynamicallyadjustable sense channel may be adjusted downward to a lower performancelevel if the indication of signal quality exceeds a threshold to helpreduce power consumption. The illustrative method may further includerepeating the sensing, operating, analyzing, determining and adjustingsteps until the indication of signal quality is determined to beacceptable.

The above summary of some illustrative embodiments is not intended todescribe each disclosed embodiment or every implementation of thepresent disclosure. The Figures, and Detailed Description, which follow,more particularly exemplify some of these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description in connection with the accompanyingdrawings, in which:

FIG. 1 is a schematic block diagram of an implantable medical device(IMD) in accordance with an example of the disclosure;

FIG. 2 is a schematic block diagram of a leadless cardiac pacemaker(LCP) in accordance with an example of the disclosure;

FIG. 3 is a schematic diagram of an illustrative logic flow that may beused in the IMD of FIG. 1 and/or the LCP of FIG. 2;

FIG. 4 is a schematic diagram of an illustrative logic flow that may beused in the IMD of FIG. 1 and/or the LCP of FIG. 2;

FIG. 5 is a schematic illustration of a cardiac signal, indicatingexample time ranges for activating a sense channel in order to reducepower consumption;

FIG. 6 is a schematic block diagram of an illustrative LCP in accordancewith an example of the disclosure;

FIG. 7 is a schematic block diagram of another illustrative medicaldevice that may be used in conjunction with the LCP of FIG. 6;

FIG. 8 is a schematic diagram of an exemplary medical system thatincludes multiple LCPs and/or other devices in communication with oneanother;

FIG. 9 is a schematic diagram of a system including an LCP and anothermedical device, in accordance with an example of the disclosure;

FIG. 10 is a side view of an illustrative implantable leadless cardiacdevice; and

FIG. 11 is a flow diagram of an illustrative method for monitoring apatient's heart using the IMD of FIG. 1 and/or the LCP of FIG. 2.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the disclosureto the particular embodiments described. On the contrary, the intentionis to cover all modifications, equivalents, and alternatives fallingwithin the spirit and scope of the disclosure.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about,” whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the terms “about” may include numbers thatare rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”,“some embodiments”, “other embodiments”, etc., indicate that theembodiment described may include one or more particular features,structures, and/or characteristics. However, such recitations do notnecessarily mean that all embodiments include the particular features,structures, and/or characteristics. Additionally, when particularfeatures, structures, and/or characteristics are described in connectionwith one embodiment, it should be understood that such features,structures, and/or characteristics may also be used connection withother embodiments whether or not explicitly described unless clearlystated to the contrary.

The following detailed description should be read with reference to thedrawings in which similar structures in different drawings are numberedthe same. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of thedisclosure.

FIG. 1 is a schematic view of an implantable medical device (IMD) 10. Insome cases, the IMD 10 may represent an insertable cardiac monitor(ICM). In some cases, the IMD 10 may represent a cardiac pacemaker suchas a leadless cardiac pacemaker (LCP). These are just examples.

Cardiac pacemakers provide electrical stimulation to heart tissue tocause the heart to contract and thus pump blood through the vascularsystem. Conventional pacemakers may include an electrical lead thatextends from a pulse generator implanted subcutaneously orsub-muscularly to an electrode positioned adjacent the inside or outsidewall of the cardiac chamber. As an alternative to conventionalpacemakers, self-contained or leadless cardiac pacemakers (LCP) havebeen proposed. Leadless cardiac pacemakers (LCP) are small capsules thatmay, for example, be fixed to an intracardiac implant site in a cardiacchamber. In some cases, the small capsule may include bipolarpacing/sensing electrodes, a power source (e.g. a battery), andassociated electrical circuitry for controlling the pacing/sensingelectrodes, and thus may provide electrical stimulation to heart tissueand/or sense a physiological condition. The capsule may be delivered tothe heart using a delivery device which may be advanced through afemoral vein, into the inferior vena cava, into the right atrium,through the tricuspid valve, and into the right ventricle. Accordingly,it may be desirable to provide delivery devices which facilitateadvancement through the vasculature.

Referring specifically to FIG. 1, and in some instances, the IMD 10includes a housing 12 and a sensor 14 that may be configured to providea sensor output signal. In some cases, the sensor 14 may be anelectrical signal sensor that senses an electric signal between, forexample, two sensor electrodes. In some instances, the sensor 14 may beone or more of an accelerometer, a pressure sensor, a gyroscope and amagnetic sensor. These are just examples. In some cases, a sense channel16 may be configured to receive the sensor output signal from the sensor14, process the sensor output signal and output a sense channel outputsignal. It is contemplated that the sensor output signal may beprocessed by an analog circuit (e.g. sense amplifier), a digital circuit(e.g. Analog-to-Digital Converter) and/or digital processor, or both. Insome cases, the sense channel 16 may have an adjustable performancelevel, wherein a higher performance level the sense channel 16 consumesmore power than a lower performance level.

A controller 18 may be configured to receive the sense channel outputsignal from the sense channel 16. In some case, the controller 18 may beconfigured to adjust the performance level of the sense channel 16 toachieve more performance (and thus more power consumption) when a higherdegree of performance is desired, and to achieve less performance (andless power consumption) when a high degree of performance is notdesired. In some cases, the controller 18 may be configured to adjustthe performance level of the sense channel 16 in accordance with one ormore received signals or other indications of the patient's postureand/or activity level. For example, if the patient is sleeping, thesense channel 16 may be operated at a lower performance level as theircardiac cycle may be expected to vary less, for example. As anotherexample, if the patient is relatively active, the sense channel 16 maybe operated at a higher performance level as their cardiac cycle may beexpected to vary more.

In some cases, the controller 18 may be configured to dynamically adjustthe performance level of the sense channel 16. In some cases, forexample, the controller 18 may be configured to determine a measure of asignal-to-noise ratio (SNR) of the sense channel output signal, andadjust the performance level of the sense channel 16 based at least inpart on the measure of the signal-to-noise ratio (SNR) of the sensechannel output signal. In another example, the IMD 10 may be configuredto sense and process two or more different cardiac signals, and thecontroller 18 may be configured to adjust the performance level of thesense channel 16 based at least in part on which of the two or moredifferent cardiac signals is to be sensed and processed. For example,the two or more different cardiac signals may include an R-wave and aP-Wave, and the controller 18 may be configured to adjust theperformance level of the sense channel 16 to achieve more performanceand more power consumption when the P-Wave is to be sensed andprocessed, and to adjust the performance level of the sense channel 16to achieve less performance and less power consumption when the R-Waveis to be sensed and processed.

In some cases, the performance level of the sense channel 16 may beincreased by increasing a noise floor and/or a bias of a sense amplifier(not explicitly shown) of the sense channel 16. In some cases, theperformance level of the sense channel may be increased by increasing asample rate of the sense channel 16. If increased sensitivity isdesired, the controller 18 may increase the sample rate of the sensechannel 16. In some cases, if increased sensitivity is desired, thecontroller 18 may increase the supply voltage to the sense channel 16.If power conservation considerations outweigh a need for sensitivity,the controller 18 may decrease the sample rate of the sense channel 16.In some cases, the sense channel 16 may be activated and deactivated ata duty cycle, and the performance level of the sense channel 16 may beadjusted by adjusting the duty cycle of the sense channel 16. In somecases, a duty cycle may correspond to a single cardiac cycle. In somecases, a duty cycle may correspond to several consecutive cardiaccycles. In some instances, for example, the duty cycle may pertain toturning off the sense channel 16 during a refractory period. As anotherexample, in some cases the duty cycle may include turning the sensechannel 16 on during a particular cardiac cycle and then turning thesense channel 16 off during a subsequent cardiac cycle. These are justexamples. In some cases, the sense channel 16 may include ananalog-to-digital (A/D) converter with an adjustable resolution, and theperformance level of the sense channel 16 may be adjusted by adjustingthe resolution and/or sample rate of the A/D converter.

A power supply 20 may provide power to the sensor 14, sense channel 16and/or controller 18. The power supply 20 may include a capacitor, abattery and/or any other suitable power storage device. In some cases,the power supply 20 may be a non-rechargeable lithium-based battery.These are just examples. In most cases, the power supply will have alimited power capacity, which limits the effective lifetime of thecorresponding implanted medical device. To extend the effective lifetimeof the implanted medical device, there is a desire to reduce batteryconsumption while still providing effective monitoring and/or deliveryof therapy to the patient.

FIG. 2 is a schematic view of a leadless cardiac pacemaker (LCP) 22 thatis configured for implantation into a patient's heart. The LCP 22 may beconfigured to sense electrical cardiac activity and to deliver pacingpulses to the patient's heart when appropriate. In some cases, the LCP22 may include a housing 24, a first electrode 26 that is securedrelative to the housing 24, and a second electrode 28 that is securedrelative to the housing 24 and that is spaced from the first electrode26. A controller 30 may be disposed within the housing 24 and may beoperably coupled to the first electrode 26 and to the second electrode28 such that the controller 30 is capable of receiving, via the firstelectrode 26 and the second electrode 28, electrical cardiac signals ofthe patient's heart. In some cases, a sensor 32 may be disposed withinthe housing 24 and may be configured to sense an indication of cardiacactivity and/or another parameter relative to the patient and to providea sensor output signal. A sense channel 34 may be configured to receivethe sensor output signal from the sensor 32 and to process (analogand/or digital) the sensor output signal in order to output a sensechannel output signal. In some cases, the sense channel 34 may have anadjustable performance level, wherein for a higher performance level thesense channel 34 consumes more power and for a lower performance levelthe sense channel 34 consumes less power.

The controller 30 may be configured to receive the sense channel outputsignal and adjust the performance level of the sense channel 34 toachieve more performance and more power consumption when a higher degreeof performance is desired and to achieve less performance and less powerconsumption when a high degree of performance is not desired. Thecontroller 30, sense channel 34 and/or sensor 32 may be operably poweredby a power supply 36.

In some cases, the sensor 32 may be an electrical signal sensor thatsenses an electric signal between the first electrode 26 and the secondelectrode 28. In some instances, the sensor 32 may be one or more of anaccelerometer, a pressure sensor, a gyroscope and a magnetic sensor.These are just some example sensors.

In some cases, the controller 30 may be configured to dynamically adjustthe performance level of the sense channel 34. In some cases, forexample, the controller 30 may be configured to determine a measure of asignal-to-noise ratio (SNR) of the sense channel output signal, andadjust the performance level of the sense channel 34 based at least inpart on the measure of the signal-to-noise ratio (SNR) of the sensechannel output signal. In another example, the LCP 22 may be configuredto sense and process two or more different cardiac signals, and thecontroller 30 may be configured to adjust the performance level of thesense channel 34 based at least in part on which of the two or moredifferent cardiac signals is to be sensed and processed. For example,the two or more different cardiac signals may include an R-wave and aP-Wave, and the controller 30 may be configured to adjust theperformance level of the sense channel 34 to achieve more performanceand more power consumption when the P-Wave is to be sensed andprocessed, and to adjust the performance level of the sense channel 34to achieve less performance and less power consumption when the R-Waveis to be sensed and processed.

In some cases, the performance level of the sense channel 34 may beincreased by increasing a noise floor and/or a bias of a sense amplifier(not explicitly shown) of the sense channel 34. In some cases, theperformance level of the sense channel 34 may be increased by increasinga sample rate of the sense channel 34. If increased sensitivity isdesired, the controller 30 may increase the sample rate of the sensechannel 34. If power conservation considerations outweigh a need forsensitivity, the controller 30 may decrease the sample rate of the sensechannel 34. In some cases, the sense channel 34 may be activated anddeactivated at a duty cycle, and the performance level of the sensechannel 34 may be adjusted by adjusting the duty cycle of the sensechannel 34. In some cases, the sense channel 34 may include ananalog-to-digital (A/D) converter with an adjustable resolution, and theperformance level of the sense channel 34 may be adjusted by adjustingthe resolution and/or sample rate of the A/D converter. These are justexamples.

FIG. 3 is a schematic diagram of an illustrative logic flow 40 that maybe used in controlling the sense channel 16 (FIG. 1) and/or the sensechannel 34 (FIG. 2). In some cases, the logic flow 40 may be consideredas including a sense signal flow block 42 and a power control feedbackblock 44. In some instances, a sense input 46 may enter the logic flow40, such as a signal from the sensor 14 (FIG. 1) and/or the sensor 32(FIG. 2) and pass through the sense channel 48. In the example shown,the sense channel 48 may function to amplify the sense input 46, andprovide a sense output signal 50 to a digital control logic block 52.The digital control logic block 52, when provided, may include anAnalog-to-Digital Converter (ADC) and/or other digital processingcircuitry. In the example shown in FIG. 3, a sense channel output signal55 exits the digital control logic block 52 and may be used by thecontroller 18 (FIG. 1) and/or controller 30 (FIG. 2 to control one ormore functions of the IMD 10 (FIG. 1) and/or LCP (FIG. 2).

In the example shown in FIG. 3, the sense channel output signal 55 isalso provided to the power control feedback block 44. The power controlfeedback block 44 may be part of the controller 18 (FIG. 1), thecontroller 30 (FIG. 2), or a separate control block. In FIG. 3, thesense channel output signal 55 is provided to a signal to noise (SNR)decision block 54 of the power control feedback block 44. The SNRdecision block 54 may determine a SNR value for the sense channel outputsignal 55, and may compare the SNR value to a threshold, standard orbaseline. In the example shown, the control block 56 may adjust theperformance level of the sense channel 48 depending on whether the SNRvalue is above or below a SNR value. In some cases, the control block 56may adjust the performance level of the sense channel 48 upward toprovide an increased signal to noise ratio (SNR Value) if the desiredsignal (e.g. P-wave) in the sense input 46 is small relative to existingnoise, or perhaps to adjust the performance level of the sense channel48 downward to reduce the signal to noise ratio (SNR value) if thedesired signal (e.g. R-wave) in the sense input 46 is relatively largerelative to existing noise. This is just one example.

FIG. 4 is a schematic diagram of an illustrative logic flow 60 that maybe used in controlling the sense channel 16 (FIG. 1) and/or the sensechannel 34 (FIG. 2). In some instances, a sense input 66 may enter thelogic flow 60, such as a signal from the sensor 14 (FIG. 1) and/or thesensor 32 (FIG. 2) and pass through the sense channel 68. In some cases,the sense channel 68 may function to amplify the sense input 66, andprovide a sense output signal 70 to a digital signal processing block72. The digital signal processing block 72, when provided, may includean Analog-to-Digital Converter (ADC) and/or other digital processingcircuitry. In the example shown in FIG. 4, a sense channel output signal75 exits the digital signal processing block 72 and may be used by thecontroller 18 (FIG. 1) and/or controller 30 (FIG. 2) to control one ormore functions of the IMD 10 (FIG. 1) and/or LCP (FIG. 2).

In the example shown in FIG. 4, the sense channel output signal 75 isalso provided to a signal to noise (SNR) decision block 74, where a SNRvalue for a desired signal in the sense channel output signal 75 isestimated or determined. A control block 76 may then adjust theperformance level of the sense channel 68 to achieve a desired SNR valuein the sense channel output signal 75. In some cases, the SNR value maybe directly measured.

Rather than directly measuring the SNR value, it is contemplated thatthe SNR decision block 74 may simply identify whether the IMD or LCP iscurrently attempting to sense a smaller signal (e.g. P-wave) that mayhave a relatively lower signal to noise ratio (SNR), or if the IMD orLCP is currently attempting to sense a larger signal (e.g. an R-wave)that may have a relatively higher signal to noise ratio (SNR). This maybe reported to the control block 76. If the IMD or LCP is currentlyattempting to sense a smaller signal, the control block 76 mayautomatically increase the performance level of the sense channel 68 atthe expense of power consumption, and if the IMD or LCP is currentlyattempting to sense a larger signal, the control block 76 may decreasethe performance level of the sense channel 68 to reduce powerconsumption. In some cases, the SNR decision block 74 may confirm thatthe resulting SNR value is sufficient.

Control block 76 may be part of a feedback path to adjust theperformance level of the sense channel 68. In some cases, the controlblock 76 may adjusted the sense channel 68 to, for example, provide anincreased signal to noise ratio (SNR value) if the sense input 66 issmall relative to existing noise, or perhaps to allow a decreased signalto noise ratio (SNR value) if the sense input 66 is relatively robustrelative to existing noise. In some cases, the decision block 74 maymonitor the sense channel output signal 75 when a desired signal is notexpected at the sense input 66 to help identify the existing noiselevel.

In some cases, the sense channel 68 may have an adjustable performancelevel. For example, a bias and/or gain of a sense amplifier of the sensechannel 68 may be adjusted as shown at block 68 a to change theperformance level of the sense channel 68. Increasing the gain mayamplifier a desired signal relative to the existing noise. In anotherexample, a sampling rate and/or resolution (number of bits) of an ADCmay be adjusted as shown at blocks 68 b and 68 c, to change theperformance level of the sense channel 68. In another example, one ormore filters (Low pass, high pass, band pass) of the sense channel 68may be activated/deactivated and/or one or more poles of one or morefilters may be adjusted, as shown at block 68 d, to help filter thenoise and thus change the performance level of the sense channel 68.These are just examples.

In some cases, a sense channel or portions thereof may be operated inaccordance with an expected timing within, for example, a cardiac cycle.For example, if a sensor operably coupled to a sense channel isconfigured to sense a P-wave, the sense channel may be configured toturn itself on or to increase its resolution, sensitivity or gainshortly before the next P-wave is expected. To illustrate, FIG. 5provides a cardiac signal trace 80 including a first QRS complex 82 anda second QRS complex 84 and a timing signal 86. In the example shown, anexpected PT time (e.g. an expected time from P-wave to T-wave) may beutilized. This is labeled as delta T0 on the timing signal 86, and maybe on the order of 300 milliseconds. In some cases, the sense channelmay be activated or placed in a higher performance mode during theperiod delta T0, and deactivated or placed in a lower performance modeoutside of the period delta T0.

In some case, the sense channel may be turned off just before the T-wave(such as about 0 to 50 milliseconds after the previous R-wave), and thenmay be turned on a time delta T1 before the P-wave. In some cases,P-wave timing may be predicted using a timing fiducial from a previouscardiac cycle, and a time period denoted as delta T2 may be subtractedfrom an R-R interval (time between a first R-wave and a second R-wave).As another option, a dynamic PT time may be used, based upon the QTinterval, which is based on the heart rate. These are just examples ofadjusting the performance level of a sense channel based on when adesired signal is expected to be present.

FIG. 6 depicts an illustrative leadless cardiac pacemaker (LCP) that maybe implanted into a patient and may operate to deliver appropriatetherapy to the heart, such as to deliver anti-tachycardia pacing (ATP)therapy, cardiac resynchronization therapy (CRT), bradycardia therapy,and/or the like. The LCP shown in FIG. 6 may include the featuresdescribed herein for adjusting the performance level of a sense channel.As can be seen in FIG. 6, the LCP 100 may be a compact device with allcomponents housed within the or directly on a housing 120. In somecases, the LCP 100 may be considered as being an example of the IMD 10(FIG. 1) and/or the LCP 22 (FIG. 2). In the example shown in FIG. 6, theLCP 100 may include a communication module 102, a pulse generator module104, an electrical sensing module 106, a mechanical sensing module 108,a processing module 110, a battery 112, and an electrode arrangement114. The LCP 100 may include more or less modules, depending on theapplication.

The communication module 102 may be configured to communicate withdevices such as sensors, other medical devices such as an SICD, and/orthe like, that are located externally to the LCP 100. Such devices maybe located either external or internal to the patient's body.Irrespective of the location, external devices (i.e. external to the LCP100 but not necessarily external to the patient's body) can communicatewith the LCP 100 via communication module 102 to accomplish one or moredesired functions. For example, the LCP 100 may communicate information,such as sensed electrical signals, data, instructions, messages, R-wavedetection markers, etc., to an external medical device (e.g. SICD and/orprogrammer) through the communication module 102. The external medicaldevice may use the communicated signals, data, instructions, messages,R-wave detection markers, etc., to perform various functions, such asdetermining occurrences of arrhythmias, delivering electricalstimulation therapy, storing received data, and/or performing any othersuitable function. The LCP 100 may additionally receive information suchas signals, data, instructions and/or messages from the external medicaldevice through the communication module 102, and the LCP 100 may use thereceived signals, data, instructions and/or messages to perform variousfunctions, such as determining occurrences of arrhythmias, deliveringelectrical stimulation therapy, storing received data, and/or performingany other suitable function. The communication module 102 may beconfigured to use one or more methods for communicating with externaldevices. For example, the communication module 102 may communicate viaradiofrequency (RF) signals, inductive coupling, optical signals,acoustic signals, conducted communication signals, and/or any othersignals suitable for communication.

In the example shown in FIG. 6, the pulse generator module 104 may beelectrically connected to the electrodes 114. In some examples, the LCP100 may additionally include electrodes 114′. In such examples, thepulse generator 104 may also be electrically connected to the electrodes114′. The pulse generator module 104 may be configured to generateelectrical stimulation signals. For example, the pulse generator module104 may generate and deliver electrical stimulation signals by usingenergy stored in the battery 112 within the LCP 100 and deliver thegenerated electrical stimulation signals via the electrodes 114 and/or114′. Alternatively, or additionally, the pulse generator 104 mayinclude one or more capacitors, and the pulse generator 104 may chargethe one or more capacitors by drawing energy from the battery 112. Thepulse generator 104 may then use the energy of the one or morecapacitors to deliver the generated electrical stimulation signals viathe electrodes 114 and/or 114′. In at least some examples, the pulsegenerator 104 of the LCP 100 may include switching circuitry toselectively connect one or more of the electrodes 114 and/or 114′ to thepulse generator 104 in order to select which of the electrodes 114/114′(and/or other electrodes) the pulse generator 104 delivers theelectrical stimulation therapy. The pulse generator module 104 maygenerate and deliver electrical stimulation signals with particularfeatures or in particular sequences in order to provide one or multipleof a number of different stimulation therapies. For example, the pulsegenerator module 104 may be configured to generate electricalstimulation signals to provide electrical stimulation therapy to combatbradycardia, tachycardia, cardiac synchronization, bradycardiaarrhythmias, tachycardia arrhythmias, fibrillation arrhythmias, cardiacsynchronization arrhythmias and/or to produce any other suitableelectrical stimulation therapy. Some more common electrical stimulationtherapies include anti-tachycardia pacing (ATP) therapy, cardiacresynchronization therapy (CRT), and cardioversion/defibrillationtherapy. In some cases, the pulse generator 104 may provide acontrollable pulse energy. In some cases, the pulse generator 104 mayallow the controller to control the pulse voltage, pulse width, pulseshape or morphology, and/or any other suitable pulse characteristic.

In some examples, the LCP 100 may include an electrical sensing module106, and in some cases, a mechanical sensing module 108. The electricalsensing module 106 may be configured to sense the cardiac electricalactivity of the heart. For example, the electrical sensing module 106may be connected to the electrodes 114/114′, and the electrical sensingmodule 106 may be configured to receive cardiac electrical signalsconducted through the electrodes 114/114′. The cardiac electricalsignals may represent local information from the chamber in which theLCP 100 is implanted. For instance, if the LCP 100 is implanted within aventricle of the heart (e.g. RV, LV), cardiac electrical signals sensedby the LCP 100 through the electrodes 114/114′ may represent ventricularcardiac electrical signals. In some cases, the LCP 100 may be configuredto detect cardiac electrical signals from other chambers (e.g. farfield), such as the P-wave from the atrium.

The mechanical sensing module 108 may include one or more sensors, suchas an accelerometer, a pressure sensor, a heart sound sensor, ablood-oxygen sensor, a chemical sensor, a temperature sensor, a flowsensor and/or any other suitable sensors that are configured to measureone or more mechanical/chemical parameters of the patient. Both theelectrical sensing module 106 and the mechanical sensing module 108 maybe connected to a processing module 110, which may provide signalsrepresentative of the sensed mechanical parameters. Although describedwith respect to FIG. 6 as separate sensing modules, in some cases, theelectrical sensing module 206 and the mechanical sensing module 208 maybe combined into a single sensing module, as desired.

The electrodes 114/114′ can be secured relative to the housing 120 butexposed to the tissue and/or blood surrounding the LCP 100. In somecases, the electrodes 114 may be generally disposed on either end of theLCP 100 and may be in electrical communication with one or more of themodules 102, 104, 106, 108, and 110. The electrodes 114/114′ may besupported by the housing 120, although in some examples, the electrodes114/114′ may be connected to the housing 120 through short connectingwires such that the electrodes 114/114′ are not directly securedrelative to the housing 120. In examples where the LCP 100 includes oneor more electrodes 114′, the electrodes 114′ may in some cases bedisposed on the sides of the LCP 100, which may increase the number ofelectrodes by which the LCP 100 may sense cardiac electrical activity,deliver electrical stimulation and/or communicate with an externalmedical device. The electrodes 114/114′ can be made up of one or morebiocompatible conductive materials such as various metals or alloys thatare known to be safe for implantation within a human body. In someinstances, the electrodes 114/114′ connected to the LCP 100 may have aninsulative portion that electrically isolates the electrodes 114/114′from adjacent electrodes, the housing 120, and/or other parts of the LCP100. In some cases, one or more of the electrodes 114/114′ may beprovided on a tail (not shown) that extends away from the housing 120.

The processing module 110 can be configured to control the operation ofthe LCP 100. For example, the processing module 110 may be configured toreceive electrical signals from the electrical sensing module 106 and/orthe mechanical sensing module 108. Based on the received signals, theprocessing module 110 may determine, for example, abnormalities in theoperation of the heart H. Based on any determined abnormalities, theprocessing module 110 may control the pulse generator module 104 togenerate and deliver electrical stimulation in accordance with one ormore therapies to treat the determined abnormalities. The processingmodule 110 may further receive information from the communication module102. In some examples, the processing module 110 may use such receivedinformation to help determine whether an abnormality is occurring,determine a type of abnormality, and/or to take particular action inresponse to the information. The processing module 110 may additionallycontrol the communication module 102 to send/receive information to/fromother devices.

In some examples, the processing module 110 may include a pre-programmedchip, such as a very-large-scale integration (VLSI) chip and/or anapplication specific integrated circuit (ASIC). In such embodiments, thechip may be pre-programmed with control logic in order to control theoperation of the LCP 100. By using a pre-programmed chip, the processingmodule 110 may use less power than other programmable circuits (e.g.general purpose programmable microprocessors) while still being able tomaintain basic functionality, thereby potentially increasing the batterylife of the LCP 100. In other examples, the processing module 110 mayinclude a programmable microprocessor. Such a programmablemicroprocessor may allow a user to modify the control logic of the LCP100 even after implantation, thereby allowing for greater flexibility ofthe LCP 100 than when using a pre-programmed ASIC. In some examples, theprocessing module 110 may further include a memory, and the processingmodule 110 may store information on and read information from thememory. In other examples, the LCP 100 may include a separate memory(not shown) that is in communication with the processing module 110,such that the processing module 110 may read and write information toand from the separate memory.

The battery 112 may provide power to the LCP 100 for its operations. Insome examples, the battery 112 may be a non-rechargeable lithium-basedbattery. In other examples, a non-rechargeable battery may be made fromother suitable materials, as desired. Because the LCP 100 is animplantable device, access to the LCP 100 may be limited afterimplantation. Accordingly, it is desirable to have sufficient batterycapacity to deliver therapy over a period of treatment such as days,weeks, months, years or even decades. In some instances, the battery 112may a rechargeable battery, which may help increase the useable lifespanof the LCP 100. In still other examples, the battery 112 may be someother type of power source, as desired.

To implant the LCP 100 inside a patient's body, an operator (e.g., aphysician, clinician, etc.), may fix the LCP 100 to the cardiac tissueof the patient's heart. To facilitate fixation, the LCP 100 may includeone or more anchors 116. The anchor 116 may include any one of a numberof fixation or anchoring mechanisms. For example, the anchor 116 mayinclude one or more pins, staples, threads, screws, helix, tines, and/orthe like. In some examples, although not shown, the anchor 116 mayinclude threads on its external surface that may run along at least apartial length of the anchor 116. The threads may provide frictionbetween the cardiac tissue and the anchor to help fix the anchor 116within the cardiac tissue. In other examples, the anchor 116 may includeother structures such as barbs, spikes, or the like to facilitateengagement with the surrounding cardiac tissue.

FIG. 7 depicts an example of another or second medical device (MD) 200,which may be used in conjunction with the LCP 100 (FIG. 6) in order todetect and/or treat cardiac abnormalities. In some cases, the MD 200 maybe considered as an example of the IMD 10 (FIG. 1) and/or the LCP 22(FIG. 2). In the example shown, the MD 200 may include a communicationmodule 202, a pulse generator module 204, an electrical sensing module206, a mechanical sensing module 208, a processing module 210, and abattery 218. Each of these modules may be similar to the modules 102,104, 106, 108, and 110 of LCP 100. Additionally, the battery 218 may besimilar to the battery 112 of the LCP 100. In some examples, however,the MD 200 may have a larger volume within the housing 220. In suchexamples, the MD 200 may include a larger battery and/or a largerprocessing module 210 capable of handling more complex operations thanthe processing module 110 of the LCP 100.

While it is contemplated that the MD 200 may be another leadless devicesuch as shown in FIG. 6, in some instances the MD 200 may include leadssuch as leads 212. The leads 212 may include electrical wires thatconduct electrical signals between the electrodes 214 and one or moremodules located within the housing 220. In some cases, the leads 212 maybe connected to and extend away from the housing 220 of the MD 200. Insome examples, the leads 212 are implanted on, within, or adjacent to aheart of a patient. The leads 212 may contain one or more electrodes 214positioned at various locations on the leads 212, and in some cases atvarious distances from the housing 220. Some leads 212 may only includea single electrode 214, while other leads 212 may include multipleelectrodes 214. Generally, the electrodes 214 are positioned on theleads 212 such that when the leads 212 are implanted within the patient,one or more of the electrodes 214 are positioned to perform a desiredfunction. In some cases, the one or more of the electrodes 214 may be incontact with the patient's cardiac tissue. In some cases, the one ormore of the electrodes 214 may be positioned subcutaneously and outsideof the patient's heart. In some cases, the electrodes 214 may conductintrinsically generated electrical signals to the leads 212, e.g.signals representative of intrinsic cardiac electrical activity. Theleads 212 may, in turn, conduct the received electrical signals to oneor more of the modules 202, 204, 206, and 208 of the MD 200. In somecases, the MD 200 may generate electrical stimulation signals, and theleads 212 may conduct the generated electrical stimulation signals tothe electrodes 214. The electrodes 214 may then conduct the electricalsignals and delivery the signals to the patient's heart (either directlyor indirectly).

The mechanical sensing module 208, as with the mechanical sensing module108, may contain or be electrically connected to one or more sensors,such as accelerometers, acoustic sensors, blood pressure sensors, heartsound sensors, blood-oxygen sensors, and/or other sensors which areconfigured to measure one or more mechanical/chemical parameters of theheart and/or patient. In some examples, one or more of the sensors maybe located on the leads 212, but this is not required. In some examples,one or more of the sensors may be located in the housing 220.

While not required, in some examples, the MD 200 may be an implantablemedical device. In such examples, the housing 220 of the MD 200 may beimplanted in, for example, a transthoracic region of the patient. Thehousing 220 may generally include any of a number of known materialsthat are safe for implantation in a human body and may, when implanted,hermetically seal the various components of the MD 200 from fluids andtissues of the patient's body.

In some cases, the MD 200 may be an implantable cardiac pacemaker (ICP).In this example, the MD 200 may have one or more leads, for example theleads 212, which are implanted on or within the patient's heart. The oneor more leads 212 may include one or more electrodes 214 that are incontact with cardiac tissue and/or blood of the patient's heart. The MD200 may be configured to sense intrinsically generated cardiacelectrical signals and determine, for example, one or more cardiacarrhythmias based on analysis of the sensed signals. The MD 200 may beconfigured to deliver CRT, ATP therapy, bradycardia therapy, and/orother therapy types via the leads 212 implanted within the heart. Insome examples, the MD 200 may additionally be configured providedefibrillation therapy.

In some instances, the MD 200 may be an implantablecardioverter-defibrillator (ICD). In such examples, the MD 200 mayinclude one or more leads implanted within a patient's heart. The MD 200may also be configured to sense cardiac electrical signals, determineoccurrences of tachyarrhythmias based on the sensed signals, and may beconfigured to deliver defibrillation therapy in response to determiningan occurrence of a tachyarrhythmia. In other examples, the MD 200 may bea subcutaneous implantable cardioverter-defibrillator (S-ICD). Inexamples where the MD 200 is an S-ICD, one of the leads 212 may be asubcutaneously implanted lead. In at least some examples where the MD200 is an S-ICD, the MD 200 may include only a single lead which isimplanted subcutaneously, but this is not required. In some instances,the lead(s) may have one or more electrodes that are placedsubcutaneously and outside of the chest cavity. In other examples, thelead(s) may have one or more electrodes that are placed inside of thechest cavity, such as just interior of the sternum but outside of theheart H.

In some examples, the MD 200 may not be an implantable medical device.Rather, the MD 200 may be a device external to the patient's body, andmay include skin-electrodes that are placed on a patient's body. In suchexamples, the MD 200 may be able to sense surface electrical signals(e.g. cardiac electrical signals that are generated by the heart orelectrical signals generated by a device implanted within a patient'sbody and conducted through the body to the skin). In such examples, theMD 200 may be configured to deliver various types of electricalstimulation therapy, including, for example, defibrillation therapy.

FIG. 8 illustrates an example of a medical device system and acommunication pathway through which multiple medical devices 302, 304,306, and/or 310 may communicate. In the example shown, the medicaldevice system 300 may include LCPs 302 and 304, external medical device306, and other sensors/devices 310. The external device 306 may be anyof the devices described previously with respect to the MD 200. Othersensors/devices 310 may also be any of the devices described previouslywith respect to the MD 200. In some instances, other sensors/devices 310may include a sensor, such as an accelerometer, an acoustic sensor, ablood pressure sensor, or the like. In some cases, other sensors/devices310 may include an external programmer device that may be used toprogram one or more devices of the system 300.

Various devices of the system 300 may communicate via communicationpathway 308. For example, the LCPs 302 and/or 304 may sense intrinsiccardiac electrical signals and may communicate such signals to one ormore other devices 302/304, 306, and 310 of the system 300 viacommunication pathway 308. In one example, one or more of the devices302/304 may receive such signals and, based on the received signals,determine an occurrence of an arrhythmia. In some cases, the device ordevices 302/304 may communicate such determinations to one or more otherdevices 306 and 310 of the system 300. In some cases, one or more of thedevices 302/304, 306, and 310 of the system 300 may take action based onthe communicated determination of an arrhythmia, such as by delivering asuitable electrical stimulation to the heart of the patient. It iscontemplated that the communication pathway 308 may communicate using RFsignals, inductive coupling, optical signals, acoustic signals, or anyother signals suitable for communication. Additionally, in at least someexamples, device communication pathway 308 may include multiple signaltypes. For instance, other sensors/device 310 may communicate with theexternal device 306 using a first signal type (e.g. RF communication)but communicate with the LCPs 302/304 using a second signal type (e.g.conducted communication). Further, in some examples, communicationbetween devices may be limited. For instance, as described above, insome examples, the LCPs 302/304 may communicate with the external device306 only through other sensors/devices 310, where the LCPs 302/304 sendsignals to other sensors/devices 310, and other sensors/devices 310relay the received signals to the external device 306.

In some cases, the communication pathway 308 may include conductedcommunication. Accordingly, devices of the system 300 may havecomponents that allow for such conducted communication. For instance,the devices of system 300 may be configured to transmit conductedcommunication signals (e.g. current and/or voltage pulses) into thepatient's body via one or more electrodes of a transmitting device, andmay receive the conducted communication signals (e.g. pulses) via one ormore electrodes of a receiving device. The patient's body may “conduct”the conducted communication signals (e.g. pulses) from the one or moreelectrodes of the transmitting device to the electrodes of the receivingdevice in the system 300. In such examples, the delivered conductedcommunication signals (e.g. pulses) may differ from pacing or othertherapy signals. For example, the devices of the system 300 may deliverelectrical communication pulses at an amplitude/pulse width that issub-capture threshold to the heart. Although, in some cases, theamplitude/pulse width of the delivered electrical communication pulsesmay be above the capture threshold of the heart, but may be deliveredduring a blanking period of the heart (e.g. refractory period) and/ormay be incorporated in or modulated onto a pacing pulse, if desired.

Delivered electrical communication pulses may be modulated in anysuitable manner to encode communicated information. In some cases, thecommunication pulses may be pulse width modulated or amplitudemodulated. Alternatively, or in addition, the time between pulses may bemodulated to encode desired information. In some cases, conductedcommunication pulses may be voltage pulses, current pulses, biphasicvoltage pulses, biphasic current pulses, or any other suitableelectrical pulse as desired.

FIG. 9 shows an illustrative medical device system. In FIG. 9, an LCP402 is shown fixed to the interior of the left ventricle of the heart410, and a pulse generator 406 is shown coupled to a lead 412 having oneor more electrodes 408 a-408 c. In some cases, the pulse generator 406may be part of a subcutaneous implantable cardioverter-defibrillator(S-ICD), and the one or more electrodes 408 a-408 c may be positionedsubcutaneously. In some cases, the one or more electrodes 408 a-408 cmay be placed inside of the chest cavity but outside of the heart, suchas just interior of the sternum.

In some cases, the LCP 402 may communicate with the subcutaneousimplantable cardioverter-defibrillator (S-ICD). In some cases, the lead412 and/or pulse generator 406 may include an accelerometer 414 thatmay, for example, be configured to sense vibrations that may beindicative of heart sounds.

In some cases, the LCP 402 may be in the right ventricle, right atrium,left ventricle or left atrium of the heart, as desired. In some cases,more than one LCP 402 may be implanted. For example, one LCP may beimplanted in the right ventricle and another may be implanted in theright atrium. In another example, one LCP may be implanted in the rightventricle and another may be implanted in the left ventricle. In yetanother example, one LCP may be implanted in each of the chambers of theheart.

FIG. 10 is a side view of an illustrative implantable leadless cardiacpacemaker (LCP) 610. The LCP 610 may be similar in form and function tothe LCP 100 described above. The LCP 610 may include any of the modulesand/or structural features described above with respect to the LCP 100described above. The LCP 610 may include a shell or housing 612 having aproximal end 614 and a distal end 616. The illustrative LCP 610 includesa first electrode 620 secured relative to the housing 612 and positionedadjacent to the distal end 616 of the housing 612 and a second electrode622 secured relative to the housing 612 and positioned adjacent to theproximal end 614 of the housing 612. In some cases, the housing 612 mayinclude a conductive material and may be insulated along a portion ofits length. A section along the proximal end 614 may be free ofinsulation so as to define the second electrode 622. The electrodes 620,622 may be sensing and/or pacing electrodes to provide electro-therapyand/or sensing capabilities. The first electrode 620 may be capable ofbeing positioned against or may otherwise contact the cardiac tissue ofthe heart while the second electrode 622 may be spaced away from thefirst electrode 620. The first and/or second electrodes 620, 622 may beexposed to the environment outside the housing 612 (e.g. to blood and/ortissue).

In some cases, the LCP 610 may include a pulse generator (e.g.,electrical circuitry) and a power source (e.g., a battery) within thehousing 612 to provide electrical signals to the electrodes 620, 622 tocontrol the pacing/sensing electrodes 620, 622. While not explicitlyshown, the LCP 610 may also include, a communications module, anelectrical sensing module, a mechanical sensing module, and/or aprocessing module, and the associated circuitry, similar in form andfunction to the modules 102, 106, 108, 110 described above. The variousmodules and electrical circuitry may be disposed within the housing 612.Electrical connections between the pulse generator and the electrodes620, 622 may allow electrical stimulation to heart tissue and/or sense aphysiological condition.

In the example shown, the LCP 610 includes a fixation mechanism 624proximate the distal end 616 of the housing 612. The fixation mechanism624 is configured to attach the LCP 610 to a wall of the heart H, orotherwise anchor the LCP 610 to the anatomy of the patient. In someinstances, the fixation mechanism 624 may include one or more, or aplurality of hooks or tines 626 anchored into the cardiac tissue of theheart H to attach the LCP 610 to a tissue wall. In other instances, thefixation mechanism 624 may include one or more, or a plurality ofpassive tines, configured to entangle with trabeculae within the chamberof the heart H and/or a helical fixation anchor configured to be screwedinto a tissue wall to anchor the LCP 610 to the heart H. These are justexamples.

The LCP 610 may further include a docking member 630 proximate theproximal end 614 of the housing 612. The docking member 630 may beconfigured to facilitate delivery and/or retrieval of the LCP 610. Forexample, the docking member 630 may extend from the proximal end 614 ofthe housing 612 along a longitudinal axis of the housing 612. Thedocking member 630 may include a head portion 632 and a neck portion 634extending between the housing 612 and the head portion 632. The headportion 632 may be an enlarged portion relative to the neck portion 634.For example, the head portion 632 may have a radial dimension from thelongitudinal axis of the LCP 610 that is greater than a radial dimensionof the neck portion 634 from the longitudinal axis of the LCP 610. Insome cases, the docking member 630 may further include a tetherretention structure 636 extending from or recessed within the headportion 632. The tether retention structure 636 may define an opening638 configured to receive a tether or other anchoring mechanismtherethrough. While the retention structure 636 is shown as having agenerally “U-shaped” configuration, the retention structure 636 may takeany shape that provides an enclosed perimeter surrounding the opening638 such that a tether may be securably and releasably passed (e.g.looped) through the opening 638. In some cases, the retention structure636 may extend though the head portion 632, along the neck portion 634,and to or into the proximal end 614 of the housing 612. The dockingmember 630 may be configured to facilitate delivery of the LCP 610 tothe intracardiac site and/or retrieval of the LCP 610 from theintracardiac site. While this describes one example docking member 630,it is contemplated that the docking member 630, when provided, can haveany suitable configuration.

It is contemplated that the LCP 610 may include one or more pressuresensors 640 coupled to or formed within the housing 612 such that thepressure sensor(s) is exposed to the environment outside the housing 612to measure blood pressure within the heart. For example, if the LCP 610is placed in the left ventricle, the pressure sensor(s) 640 may measurethe pressure within the left ventricle. If the LCP 610 is placed inanother portion of the heart (such as one of the atriums or the rightventricle), the pressures sensor(s) may measure the pressure within thatportion of the heart. The pressure sensor(s) 640 may include a MEMSdevice, such as a MEMS device with a pressure diaphragm andpiezoresistors on the diaphragm, a piezoelectric sensor, acapacitor-Micro-machined Ultrasonic Transducer (cMUT), a condenser, amicro-monometer, or any other suitable sensor adapted for measuringcardiac pressure. The pressures sensor(s) 640 may be part of amechanical sensing module described herein. It is contemplated that thepressure measurements obtained from the pressures sensor(s) 640 may beused to generate a pressure curve over cardiac cycles. The pressurereadings may be taken in combination with impedance measurements (e.g.the impedance between electrodes 620 and 622) to generate apressure-impedance loop for one or more cardiac cycles as will bedescribed in more detail below. The impedance may be a surrogate forchamber volume, and thus the pressure-impedance loop may berepresentative for a pressure-volume loop for the heart H.

In some embodiments, the LCP 610 may be configured to measure impedancebetween the electrodes 620, 622. More generally, the impedance may bemeasured between other electrode pairs, such as the additionalelectrodes 114′ described above. In some cases, the impedance may bemeasure between two spaced LCP's, such as two LCP's implanted within thesame chamber (e.g. LV) of the heart H, or two LCP's implanted indifferent chambers of the heart H (e.g. RV and LV). The processingmodule of the LCP 610 and/or external support devices may derive ameasure of cardiac volume from intracardiac impedance measurements madebetween the electrodes 620, 622 (or other electrodes). Primarily due tothe difference in the resistivity of blood and the resistivity of thecardiac tissue of the heart H, the impedance measurement may vary duringa cardiac cycle as the volume of blood (and thus the volume of thechamber) surrounding the LCP changes. In some cases, the measure ofcardiac volume may be a relative measure, rather than an actual measure.In some cases, the intracardiac impedance may be correlated to an actualmeasure of cardiac volume via a calibration process, sometimes performedduring implantation of the LCP(s). During the calibration process, theactual cardiac volume may be determined using fluoroscopy or the like,and the measured impedance may be correlated to the actual cardiacvolume.

In some cases, the LCP 610 may be provided with energy deliverycircuitry operatively coupled to the first electrode 620 and the secondelectrode 622 for causing a current to flow between the first electrode620 and the second electrode 622 in order to determine the impedancebetween the two electrodes 620, 622 (or other electrode pair). It iscontemplated that the energy delivery circuitry may also be configuredto deliver pacing pulses via the first and/or second electrodes 620,622. The LCP 610 may further include detection circuitry operativelycoupled to the first electrode 620 and the second electrode 622 fordetecting an electrical signal received between the first electrode 620and the second electrode 622. In some instances, the detection circuitrymay be configured to detect cardiac signals received between the firstelectrode 620 and the second electrode 622.

When the energy delivery circuitry delivers a current between the firstelectrode 620 and the second electrode 622, the detection circuitry maymeasure a resulting voltage between the first electrode 620 and thesecond electrode 622 (or between a third and fourth electrode separatefrom the first electrode 620 and the second electrode 622, not shown) todetermine the impedance. When the energy delivery circuitry delivers avoltage between the first electrode 620 and the second electrode 622,the detection circuitry may measure a resulting current between thefirst electrode 620 and the second electrode 622 (or between a third andfourth electrode separate from the first electrode 620 and the secondelectrode 622) to determine the impedance.

FIG. 11 is a flow diagram showing an illustrative method 700 ofmonitoring a patient's heart using an implantable medical device (suchas, but not limited to, the IMD 10 of FIG. 1, the LCP of FIG. 2, the LCPof FIG. 6, the LCP of FIG. 10) that is configured for implantationproximate the patient's heart and that includes a sensor configured tosense an indication of cardiac activity and a dynamically adjustablesense channel configured to process a signal from the sensor. Theimplantable medical device may further include a controller todynamically adjust the performance level of the sense channel. Asgenerally seen at block 702, an indication of cardiac activity may besensed using the sensor. The sensor outputs a signal to the dynamicallyadjustable sense channel. The dynamically adjustable sense channel maybe operated at a performance level to process the signal from the sensorand output the processed signal to the controller, as indicated at block704. In some cases, and as seen at block 706, the processed signal maybe analyzed for an indication of signal quality and a determination maybe made as to whether the indication of signal quality is acceptable, asindicated at block 708. In some cases, and as seen at block 710, theperformance level of the dynamically adjustable sense channel may beadjusted upward if the indication of signal quality is not acceptable.In some cases, the performance level of the dynamically adjustable sensechannel may be adjusted downward to a lower performance level if theindication of signal quality exceeds a threshold in order to help reducepower consumption of the implantable medical device. In some cases,these steps may be repeated until the indication of signal quality isdetermined to be acceptable, as indicated by a dashed control line 712.

It should be understood that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size, and arrangement of steps without exceeding the scope of thedisclosure. This may include, to the extent that it is appropriate, theuse of any of the features of one example embodiment being used in otherembodiments. The disclosure's scope is, of course, defined in thelanguage in which the appended claims are expressed.

What is claimed is:
 1. An implantable medical device (IMD) comprising: ahousing; a sensor for providing a sensor output signal; a sense channelreceiving the sensor output signal from the sensor, the sense channelprocessing the sensor output signal and outputting a sense channeloutput signal; the sense channel having an adjustable performance level,wherein for a higher performance level the sense channel consumes morepower and for a lower performance level the sense channel consumes lesspower; a controller receiving the sense channel output signal; and thecontroller adjusting the performance level of the sense channel toachieve more performance and more power consumption when a higher degreeof performance is desired and to achieve less performance and less powerconsumption when a high degree of performance is not desired.
 2. The IMDof claim 1, wherein the controller determines a measure of asignal-to-noise ratio (SNR) of the sense channel output signal, andadjusts the performance level of the sense channel based at least inpart on the measure of the signal-to-noise ratio (SNR) of the sensechannel output signal.
 3. The IMD of claim 1, wherein the performancelevel of the sense channel is adjusted by adjusting a noise floor of asense amplifier of the sense channel.
 4. The IMD of claim 1, wherein theperformance level of the sense channel is adjusted by adjusting aresolution of the sense channel and/or a supply voltage of a senseamplifier of the sense channel.
 5. The IMD of claim 1, wherein theperformance level of the sense channel is adjusted by adjusted a samplerate of the sense channel.
 6. The IMD of claim 1, wherein the sensechannel comprises a sense amplifier, and wherein the performance levelof the sense channel is adjusted by adjusting a bias of the senseamplifier.
 7. The IMD of claim 1, wherein the sense channel is activatedand deactivated at a duty cycle, and wherein the performance level ofthe sense channel is adjusted by adjusting the duty cycle of the sensechannel.
 8. The IMD of claim 1, wherein the sense channel samples thesensor output signal at a sample rate, and wherein the performance levelof the sense channel is adjusted by adjusting the sample rate of thesense channel.
 9. The IMD of claim 1, wherein the sense channelcomprises an analog-to-digital (A/D) converter with an adjustableresolution, and wherein the performance level of the sense channel isadjusted by adjusting the resolution of the A/D converter.
 10. The IMDof claim 1, wherein the IMD senses and processes two or more differentcardiac signals, and wherein the controller adjusts the performancelevel of the sense channel based at least in part on which of the two ormore different cardiac signals is to be sensed and processed.
 11. TheIMD of claim 10, wherein the two or more different cardiac signalscomprise an R-wave and a P-Wave, and wherein the controller adjusts theperformance level of the sense channel to achieve more performance andmore power consumption when the P-Wave is to be sensed and processed,and adjusts the performance level of the sense channel to achieve lessperformance and less power consumption when the R-Wave is to be sensedand processed.
 12. The IMD of claim 1, wherein the controllerdynamically adjusts the performance level of the sense channel.
 13. TheIMD of claim 1, comprising a leadless cardiac pacemaker (LCP).
 14. TheIMD of claim 1, comprising an insertable cardiac monitor (ICM).
 15. Aleadless cardiac pacemaker (LCP) configured for implantation into apatient's heart, the LCP configured to sense electrical cardiac activityand to deliver pacing pulses to the patient's heart, the LCP comprising:a housing; a first electrode secured relative to the housing; a secondelectrode secured relative to the housing, the second electrode spacedfrom the first electrode; a controller disposed within the housing andoperably coupled to the first electrode and the second electrode suchthat the controller is capable of receiving, via the first electrode andthe second electrode, electrical cardiac signals of the heart; a sensordisposed within the housing, the sensor sensing an indication of cardiacactivity and providing a sensor output signal; a sense channel receivingthe sensor output signal from the sensor, the sense channel processingthe sensor output signal and outputting a sense channel output signal;the sense channel having an adjustable performance level, wherein for ahigher performance level the sense channel consumes more power and for alower performance level the sense channel consumes less power; thecontroller receiving the sense channel output signal; and the controlleradjusting the performance level of the sense channel to achieve moreperformance and more power consumption when a higher degree ofperformance is desired and to achieve less performance and less powerconsumption when a high degree of performance is not desired.
 16. TheLCP of claim 15, wherein the LCP senses and processes two or moredifferent cardiac signals, and wherein the controller adjusts theperformance level of the sense channel based at least in part on whichof the two or more different cardiac signals is to be sensed andprocessed.
 17. The LCP of claim 15, wherein the sensor comprises anelectrical signal sensor that senses an electric signal between thefirst electrode and the second electrode.
 18. The LCP of claim 15,wherein the sensor comprises one or more of an accelerometer, a pressuresensor, a gyroscope, and a magnetic sensor.
 19. A method of monitoring apatient's heart using an implantable medical device configured forimplantation proximate the patient's heart, the implantable medicaldevice including a sensor configured to sense an indication of cardiacactivity and a dynamically adjustable sense channel configured toprocess a signal from the sensor, the implantable medical device furtherincluding a controller operably coupled to the dynamically adjustablesense channel, the method comprising: sensing an indication of cardiacactivity using the sensor, the sensor outputting a signal to thedynamically adjustable sense channel; operating the dynamicallyadjustable sense channel at a performance level to process the signalfrom the sensor and output the processed signal to the controller;analyzing the processed signal for an indication of signal quality;determining if the indication of signal quality is acceptable; andadjusting the performance level of the dynamically adjustable sensechannel if the indication of signal quality is not acceptable.
 20. Themethod of claim 19, further comprising: repeating the sensing,operating, analyzing, determining and adjusting steps until theindication of signal quality is determined to be acceptable.